Bio-fuel cell

ABSTRACT

A bio-fuel cell includes at least one bio-fuel cell element. The bio-fuel cell element includes an anode, a cathode, an anode container filled with the bio-fuel, a proton exchange membrane sandwiched between the anode and the cathode, and a guide plate. The cathode includes a catalyst layer. The catalyst layer includes a number of tube carriers having electron conductibility, a number of catalyst particles uniformly adsorbed on inner wall of each of the tube carriers, and proton conductor filled in each of the tube carriers. The tube carriers cooperatively define a number of reaction gas passages. One end of each of the tube carriers connects with the proton exchange membrane. The guide plate is disposed on a surface of the cathode away from the proton exchange membrane.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201110252831.4, filed on Aug. 30, 2011, inthe China Intellectual Property Office, the contents of which are herebyincorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to a bio-fuel cell.

2. Description of Related Art

A fuel cell is a power generating device which can convert chemicalenergy into electrical energy through an electrochemical reaction of afuel and a catalyst. In a bio-fuel cell, an organic material is used asa biofuel, an enzyme is used as the catalyst. In the process of usingthe bio-fuel cell, the chemical energy of the organic material isdirectly converted into electrical energy.

The bio-fuel cell commonly includes a membrane electrode assemblyincluding a cathode, an anode, and a proton exchange membrane sandwichedbetween the cathode and the anode, an anode container filled withbio-fuel, a flow guide plate disposed on a surface of the protonexchange membrane away from the cathode, and a gas supply and suctiondevice connected with the flow guide plate. The gas supply and suctiondevice introduce a reaction gas into the cathode and suction out areaction product (e.g. water) from the cathode. The anode is immersedinto the anode container and includes a carbon fiber paper and enzymecatalyst particles distributed on the carbon fiber paper. The cathodeincludes a catalyst layer and a gas diffusion layer. The catalyst layeris sandwiched between the catalyst layer and the proton exchangemembrane. The catalyst layer commonly includes a catalyst, a catalystcarrier, a proton conductor, and an adhesive. In general, the catalystcarrier is carbon particles, and the catalyst is nano-scale preciousmetal particles uniformly dispersed in the catalyst carrier. A catalyticefficiency of the catalyst layer can influence the property of the fuelcell. The catalytic efficiency can be increased by increasing thethree-phase reaction interfaces between the precious metal particles andreaction gas, proton and electrons. The protons and electrons generatedby the anode, and the reaction gas introduced into the cathode need tobe transferred to the surfaces of the catalyst for executing theelectrochemical reaction. If the transfer passages are obstructed, theelectrochemical reaction of the bio-fuel cell will be frustrated.

The catalyst layer is commonly formed on the surfaces of the gasdiffusion layer and the proton exchange membrane by brush coating,spraying, or printing. The catalyst layer has a disordered stackstructure composed of a plurality of aggregates. It is difficult tocatalyze the electrochemical reaction because the precious metalparticles are embedded in the aggregates. Thus, the utilization rate ofthe catalyst in the catalyst layer having the disordered stack structureis low.

What is needed, therefore, is to provide a bio-fuel cell having a highcatalyst utilization rate.

BRIEF DESCRIPTION OF THE DRAWING

Many aspects of the present disclosure can be better understood withreference to the following drawings. The components in the drawings arenot necessarily to scale, the emphasis instead being placed upon clearlyillustrating the principles of the present embodiments.

FIG. 1 is a structural view of one embodiment of a bio-fuel cell.

FIG. 2 is a structural view of one embodiment of a membrane electrodeassembly having a network structure composed of a plurality of tubecarriers intersected with each other.

FIG. 3 is a structural view of another embodiment of a membraneelectrode assembly including a plurality of tube carriers havingdifferent shapes.

FIG. 4 is a structural view of yet another embodiment of a membraneelectrode assembly including a plurality of tube carriers substantiallyparallel to each other and spaced from each other.

FIG. 5 is a structural view of an anode of the bio-fuel cell of FIG. 1.

FIG. 6 is a structural view of another embodiment of a bio-fuel cell.

FIG. 7 is a structural view of yet another embodiment of a bio-fuelcell.

FIG. 8 is a schematic view of a process for making the cathode of thebio-fuel cell.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “another,” “an,” or “one” embodiment in this disclosure are notnecessarily to the same embodiment, and such references mean at leastone.

Referring to FIGS. 1 to 4, one embodiment of a bio-fuel cell 200includes at least one bio-fuel cell element 100. The fuel cell element100 includes a membrane electrode assembly 10, an anode container 24,and a guide plate 22. The membrane electrode assembly 10 includes aproton exchange membrane 12, an anode 13, and a cathode 14. The protonexchange membrane 12 is sandwiched between the anode 13 and the cathode14. The guide plate 22 is disposed on a surface of the cathode 14 awayfrom the proton exchange membrane 12. The anode container 24 is filledwith a bio-fuel 21. The anode 13 is immersed in the bio-fuel 21 of theanode container 24.

Referring to FIGS. 2 to 4, in the membrane electrode assembly 10, thecathode 14 includes a catalyst layer 16. The catalyst layer 16 is incontact with a surface of the proton exchange membrane 12. The catalystlayer 16 includes a plurality of tube carriers 162, a plurality ofcatalyst particles 164, and a proton conductor 166. The plurality ofcatalyst particles 164 are uniformly adsorbed on inner walls of the tubecarriers 162. The proton conductor 166 is filled in the plurality oftube carriers 162. The plurality of tube carriers 162 are disposed onthe surface of the proton exchange membrane 12 and cooperatively definea plurality of reaction gas passages. The reaction gas can directlydiffuse to the surfaces of the catalyst particles 164 through thereaction gas passages. The tube carriers 162 can be a porous tubestructure having electron conductibility. One end of each of the tubecarriers 162 connects with the proton exchange membrane 12, by which theproton conductor 166 filled in the tube carriers 162 can be in contactwith the proton exchange membrane 12.

The proton exchange membrane 12 can define passages to transfer protonsbetween the anode 13 and the cathode 14. The proton exchange membrane 12is disposed between the anode 13 and the cathode 14, such that the anode13 and the cathode 14 cannot be in contact with each other. A materialof the proton exchange membrane 12 can be a proton exchange resincontaining sulfoacid group. The proton exchange resin can beperfluorosulfonic acid resin or sulfonate polymer having a protonexchange function or excellent thermal stability. The sulfonate polymercan be sulfonated polyether sulphone resin, sulfonated polyphenylenesulfide resin, sulfonated polybenzimidazole resin, sulfonated phosphorusenrichment nitriles resin, sulfonated polyimide resin, sulfonatedpolystyrene-polyethylene copolymer resin, or any combination thereof. Athickness of the proton exchange membrane 12 can be in a range fromabout 10 microns (μm) to 200 μm (e.g. 18 μm to 50 μm). In oneembodiment, the proton exchange membrane 12 is perfluorosulfonic acidresin having a thickness of about 25 μm.

The plurality of tube carriers 162 can be used to connect the guideplate 22 with the proton exchange membrane 12. The plurality of tubecarriers 162 in the catalyst layer 16 can be orderly or disorderlyarranged. The plurality of reaction gas passages defined by the tubecarriers 162 is a plurality of gaps defined between the tube carriers162 and a plurality of holes defined by the tube wall of the tubecarriers 162. The reaction gas can reach the tube walls of the tubecarriers through the gaps. Furthermore, the reaction gas can diffuseinto the tube carriers 162 to contact the catalyst particles 164adsorbed on the inner walls of the tube carriers 162 through the holeson the tube walls. The tube carriers 162 can be spaced from each otherto define the plurality of reaction gas passages between the tubecarriers 162, or the tube carriers 162 can intersect each other to forma network having a plurality of holes. A shape of each of the tubecarriers 162 is not limited and can be straight, curvy, “V” shaped, or“Y” shaped. Referring to FIG. 2, in one embodiment, the tube carriers162 in membrane electrode assembly 10 intersect each other to form anetwork having a plurality of holes. Referring to FIG. 3, in oneembodiment, the tube carriers 162 in the membrane electrode assembly 10are spaced from each other and have different shapes. Referring to FIG.3, in one embodiment, all the tube carriers 162 in the membraneelectrode assembly 10 are straight shaped and substantiallyperpendicular to the surface of the proton exchange membrane 12, and theplurality of tube carriers 162 are uniformly distributed, parallel toeach other, and spaced from each other.

A diameter of the tube carrier 162 can be in a range from about 10nanometers (nm) to about 10 μm. In one embodiment, the diameter of thetube carriers 162 is in a range from about 50 nm to about 300 nm. Themore the catalyst particles 164 in the catalyst layer 16 per unitvolume, the larger the cross section of the proton conductor 166 filledin the tube carrier 162, the smaller the impedance of the protonconductor 166, and the higher the conductibility of the protons. Thetube carrier 162 can be a carbon nanotube, titanium dioxide nanotube,zinc oxide nanotube, cobalt oxide nanotube, or vanadic oxide nanotube.If the tube carrier 162 is a carbon nanotube, the carbon nanotube can bea single-walled carbon nanotube, double-walled carbon nanotube, ormulti-walled carbon nanotube. A wall thickness of the tube carrier 162can be in a range from about 1 nm to about 50 nm. The wall thickness ofthe tube carrier 162 can influence the performance of the membraneelectrode assembly 10. In one embodiment, the wall thickness of the tubecarrier 162 is in a range from about 2 nm to about 15 nm. If the wallthickness is small, the tube carrier 162 has excellent electronconductibility, and the diffusion path through which the reaction gasdiffuses in the tube carrier 162 is short. A thickness of the catalystlayer 16 can be in a range from about 1 μm to about 100 μm. A length ofthe tube carrier 162 is not limited. If the tube carrier 162 is straightline shaped and substantially perpendicular to the surface of the protonexchange membrane 12, the length of the tube carrier 16 is substantiallyequal to the thickness of the catalyst layer 16. A width of the gapsbetween the tube carriers 162 is not limited. If the plurality of tubecarriers 162 are substantially parallel to each other and spaced fromeach other, a distance between the adjacent tube carriers 162 can beless than 50 μm. In one embodiment, the tube carrier 162 is a carbonnanotube composed of amorphous carbon, the length of the carbon nanotubeis about 7 μm, the diameter of the carbon nanotube is about 100 nm, thewall thickness of the carbon nanotube is about 3 nm, and the distancebetween adjacent carbon nanotubes is about 100 nm.

The catalyst particles 164 can be precious metal particles having highcatalytic activity. The catalyst particles 164 can be platinum (Pt),palladium (Pd), aurum (Au), ruthenium (Ru) or any combination thereof.In one embodiment, the catalyst particles 164 are Pt particles. In oneembodiment, a diameter of the catalyst particles is in a range fromabout 1 nm to about 8 nm. The catalyst particles 164 are uniformlyadsorbed or are adhered on the inner wall of the tube carrier 162. Aquantity of the catalyst particles 164 in the cathode 14 can be lessthan or equal to 0.5 mg·cm⁻². In addition, the catalyst particles 164can be uniformly and stably adsorbed on the inner walls of the tubecarriers 162 and cannot easily move because the tube carriers 162 havesmall diameter and the walls of the tube carriers 162 have adsorbility.In one embodiment, the quantity of the catalyst particles 164 is 0.1mg·cm⁻², and the diameter of the catalyst particles 164 is about 3 nm.

The proton conductor 166 transfers the protons and fills in the tubecarriers 162. A material of the proton conductor 166 can be protonexchange resin containing sulfoacid group. The proton exchange resin canbe perfluorosulfonic acid resin or sulfonate polymer having protonexchange function and excellent thermal stability. The sulfonate polymercan be sulfonated polyether sulphone resin, sulfonated polyphenylenesulfide resin, sulfonated polybenzimidazole resin, sulfonated phosphorusenrichment nitriles resin, sulfonated polyimide resin, sulfonatedpolystyrene-polyethylene copolymer resin, or any combination thereof.The material of the proton conductor 166 can be different from or thesame as the material of the proton exchange membrane 12.

In the catalyst layer 16, the walls of the tube carriers 162 haveelectron conductibility, the proton conductor 166 filled in the tubecarriers 162 has proton conductibility, and the catalyst particles 164between the proton conductor 166 and the tube carriers 162 havecatalytic activity. The proton exchange membrane 12 directly connectswith the proton conductor 166 in the tube carriers 162. The gaps betweenthe tube carriers 162 can provide the reaction gas passages. The protonconductor 166 cannot obstruct the reaction gas to reach the surfaces ofthe catalyst particles 164 adsorbed on the inner wall of the tubecarriers 162.

Furthermore, each of the anode 13 and the cathode 14 can include a gasdiffusion layer 18 disposed on one end of the catalyst layer 16 awayfrom the proton exchange membrane 12. The gas diffusion layer 18 and thewalls of the tube carriers 162 in the catalyst layer 16 are electricallycontacted with each other. The gas diffusion layer 18 can support thecatalyst layer 16, collect current, transfer gas, and expel water. Amaterial of the gas diffusion layer 18 is porous conductive material.The gas diffusion layer 18 can be a carbon fiber paper or a carbonnanotube film comprising of a plurality of carbon nanotubes. A thicknessof the gas diffusion layer 18 can be in a range from about 100 μm toabout 500 μm. In addition, the tube carriers 162 in the catalyst layer16 have electron conductibility, and the tube carriers 162 define theplurality of reaction gas passages. Thus, the gas diffusion layer 18 canbe optional.

Referring to FIG. 5, the anode 13 includes a catalyst carrier 132 andenzyme catalyst 134 distributed on the catalyst carrier 132. Thecatalyst carrier 132 directly contacts the proton exchange membrane 12.The catalyst carrier 132 can support the enzyme catalyst 134 andtransfer electrons. The catalyst carrier 132 can be graphite, carbonfiber paper, or carbon nanotube film including the carbon nanotubes. Theparticles of enzyme catalyst 134 are uniformly adsorbed on the catalystcarrier 132. The enzyme catalyst 134 can catalyze the bio-fuel. Theenzyme catalyst 134 can be oxidase containing prosthetic group FAD, ordehydrogenize containing prosthetic group NAD(P)⁺. In one embodiment,the catalyst carrier 132 is a carbon nanotube film consisting of aplurality of entangled carbon nanotubes, the enzyme catalyst 134 isglucose oxidase. The anode container 24 is filled with the bio-fuel 21.The anode 13 is immersed in the bio-fuel of the anode container 24. Inone embodiment, the bio-fuel 21 is a glucose solution. Furthermore, theanode 13 further includes a proton conductor. The proton conductor, thecatalyst carrier 132, and the enzyme catalyst 134 are uniformly mixed. Amaterial of the proton conductor can transfer the protons and can be thesame as or different from the material of the proton conductor 166 ofthe cathode 14.

A structure of the anode 13 can be similar to the structure of thecathode 14. The structure of the catalyst carrier 132 can be the same asthe structure of the tube carriers 162 in the cathode 14. The enzymecatalyst 134 can be adsorbed on inner walls of the catalyst carrier 132.In this embodiment, the anode 13 can include the catalyst carrier 132,the enzyme catalyst 134, and the proton conductor. The catalyst carrier132 is disposed on the surface of the proton exchange membrane 12. Theenzyme catalyst 134 is uniformly adsorbed on the inner walls of thecatalyst carrier 132. The proton conductor is filled in the catalystcarrier 132. The catalyst carrier 132 defines a plurality of bio-fuelpassages to transfer the bio-fuel to the surface of the enzyme catalyst134. The catalyst carrier 132 can be porous tube carriers havingelectron conductibility. One end of the catalyst carriers 132 connectswith the proton exchange membrane 12, by which the proton conductorfilled in the tube carriers 132 can be in contact with the protonexchange membrane 12.

The guide plate 22 is disposed on a surface of the cathode 14 away fromthe proton exchange membrane 12. If the cathode 14 includes the gasdiffusion layer 18, the guide plate 22 is disposed on the gas diffusionlayer 18 of the cathode 14. The guide plate 22 can be used to introducethe reaction gas and expel out reaction resultant or water. The guideplate 22 has at least one flow guide groove 220 on the surface near theproton exchange membrane 12. The flow guide groove 220 can introducereaction gas into the cathode 14, and expel out the reaction resultantor water from the cathode 14. A shape of the flow guide groove 220 isnot limited. The flow guide groove 220 can be arranged to connect withthe cathode 14. In one embodiment, the flow guide groove 220 is arectangular groove. In addition, the guide plate 22 electricallycontacts with the cathode 14, and capable of transferring the electronsgenerated by the membrane electrode assembly 10 to an external circuit.A material of the guide plate 22 can be conductive material. Theconductive material can be metal or conductive carbon material. Themetal can be aluminum, copper, or iron.

Furthermore, the bio-fuel cell element 100 can include a gas supply andsuction device 30. The gas supply and suction device 30 connects withthe flow guide groove 220 of the guide plate 22. The gas supply andsuction device 30 includes a blower (not shown), pipes 31, and a valve(not shown). The blower of the gas supply and suction device 30 can beconnected with the flow guide grooves 220 of the guide plate 22 by thepipes 31. The blower can be used to provide the reaction gas. Thereaction gas can include fuel gas and oxidizing agent gas. In oneembodiment, the oxidizing agent gas is oxygen or air.

Furthermore, the bio-fuel cell element 100 can include a currentcollecting plate 26 disposed on a surface of the guide plate 22 awayfrom the proton exchange membrane 12 and electrically contacting withthe guide plate 22. The current collecting plate 26 can collect andtransfer electrons. A material of the current collecting plate 26 can bea conductive material. The conductive material can be metal orconductive carbon material. The metal can be aluminum, copper, or iron.

In the working process of the bio-fuel cell 200, a reaction of bio-fuel(e.g. glucose) in the anode container 24 can be executed under thecatalysis of the enzyme catalyst 134. An equation of the reaction can beas follows: glucose→ gluconic acid+2H⁺+2 e. The hydrogen ions producedby the above reaction are transferred to the proton exchange membrane 12through the glucose solution in the anode container 24, and thentransferred to the cathode 14 contacting the proton exchange membrane12. In addition, the electrons produced by the above reaction can betransferred to the external circuit, and then transferred to the cathode14 through the external circuit.

In addition, if the structure of the anode 13 is similar to thestructure of the cathode 14, the bio-fuel 21 can be sufficientlydiffused to the surface of the enzyme catalyst 134. In one embodiment,the catalyst carrier 132 includes a plurality of carbon nanotubes. Thebio-fuel 21 can sufficiently diffuse to the position of outer walls ofthe carbon nanotubes through the gaps between the carbon nanotubes, andthen rapidly diffuse in the inner walls of the carbon nanotubes throughholes on the wall of the carbon nanotubes. The enzyme catalyst 134 isuniformly adsorbed on the inner walls of the carbon nanotubes, so thatthe bio-fuel diffused in the carbon nanotubes can sufficiently contactthe enzyme catalyst 134. The protons and the electrons can be formed bythe reaction of the bio-fuel under the catalysis of the enzyme catalyst134. The protons can be transferred to the proton exchange membrane 12through the proton conductor filled in the carbon nanotubes, andtransferred to the cathode 14 contacting the proton exchange membrane12. The electrons produced can be transferred to the external circuit bythe walls of the carbon nanotubes because the amorphous carbon haselectron conductibility.

On the other end of the bio-fuel cell 200, the oxidizing agent gas (e.g.oxygen gas, O₂) is introduced into the cathode 14 by the supply andsuction device 30 through the flow guide groove 220 of the guide plate22. The oxygen is in contact with the catalyst layer 16 through the gasdiffusion layer 18. The electrons produced in the anode 13 aretransferred to the current collecting plate 22 by the external circuit,and the current collecting plate 22 transfers the electrons to thecathode 14. In one embodiment, the tube carriers 162 in the catalystlayer 16 are carbon nanotubes. Specifically, the oxygen gas is diffusedto the catalyst layer 16 through the gas diffusion layer 18. In thecatalyst layer 16, the oxygen gas can rapidly diffuse through the gapsdefined by the plurality of carbon nanotubes. Furthermore, the oxygengas can rapidly diffuse in the carbon nanotubes through the holes on thewalls of the carbon nanotubes composed of porous amorphous carbon. Thus,the oxygen gas can directly contact the catalyst particles 164 adsorbedon the walls of the carbon nanotubes. The electrons can be transferredto the surfaces of the catalyst particles 164 through the porousamorphous carbon of the carbon nanotubes. The hydrogen ions produced inthe anode 13 can be transferred to the surfaces of the catalystparticles 164 through the proton conductor 166 directly contacted withthe proton exchange membrane 12. Thus, the oxygen gas, the hydrogenions, and the electrons are in contact with the catalyst particles 164.A reaction of the oxygen gas, the hydrogen ions, and the electrons canbe executed under the catalysis of the catalyst particles 164. Anequation of the reaction can be as follows: ½O₂+2H⁺+2 e→H₂O. The waterproduced by the above reaction can diffuse to the gaps between thecarbon nanotubes through the walls of the carbon nanotubes, and thendiffuse to the gas diffusion layer 18 and flow out the fuel cell 100 bythe flow guide grooves 220 of the guide plate 22.

In the above use process of the bio-fuel cell 200, an electric potentialdifference is formed between the anode 13 and the cathode 14. If a loadis connected with the external circuit, a current will be formed. Inaddition, the catalyst particles 164 in the cathode 14 are uniformly andstably adsorbed on the inner walls of the carbon nanotubes. The protonconductor 166 is filled in the carbon nanotube. Thus, the protonconductor 166 cannot obstruct the reaction gas to reach the surfaces ofthe catalyst particles 164, and the oxygen, the hydrogen ions, and theelectrons can sufficiently contact with the catalyst particles 164. Theutilization rate of the catalyst particles 164 can reach about 100%.

Referring to FIG. 6, a bio-fuel cell 300 of another embodiment includesa plurality of bio-fuel cell elements 100 connected with each other inseries. The anode 13 of each bio-fuel cell element 100 is electricallyconnected with the cathode 14 of another bio-fuel cell element 100. Inone embodiment, the anode 13 of each bio-fuel cell element 100 iselectrically connected with the guide plate 22 of another bio-fuel cellelement 100 by a conductive wire. The plurality of bio-fuel cellelements 100 are connected in series.

If the plurality of bio-fuel cell elements 100 is electrically connectedwith each other in series, the output voltage of the bio-fuel cell 300is a summation of the output voltage of the plurality of bio-fuel cellelements 100.

Referring to FIG. 7, another embodiment of a bio-fuel cell 400 includesa plurality of bio-fuel cell elements 100 connected with each other inparallel. The anodes 13 of the plurality of bio-fuel cell elements 100can be electrically connected with each other. The cathodes 14 of theplurality of bio-fuel cell elements 100 can be electrically connectedwith each other. In one embodiment, the current collecting plates 26 orthe guide plates 22 electrically connected with the cathodes 14 of theplurality of bio-fuel cell elements 100 are electrically connected witheach other by conductive wires, and the anodes 13 of the plurality ofbio-fuel cell elements 100 are electrically connected with each other byconductive wires. The output voltage of the bio-fuel cell 400 is theoutput voltage of each bio-fuel cell element 100. The output current ofthe bio-fuel cell 400 is a summation of the output current of theplurality of bio-fuel cell elements 100.

Referring to FIG. 8, a method for making the cathode 14 includes thefollowing steps:

-   -   S1, providing a porous template 20 having a plurality of holes        and the proton exchange membrane 12;    -   S2, forming the tube carriers 162 having electron conductibility        in the holes of the porous template 20;    -   S3, uniformly adsorbing a plurality of catalyst particles 164 on        the inner walls of the tube carriers 162;    -   S4, filling the proton conductor 166 in the tube carriers 162        adsorbing the catalyst particles 164;    -   S5, disposing the proton exchange membrane 12 on the porous        templates 20 to form a laminated structure, and hot pressing the        laminated structure;    -   S6, removing the porous templates 20 from the laminated        structure, thereby forming the cathode 14, wherein the proton        conductor 166 is filled in the tube carriers 162 adsorbing the        catalyst particles 164, first ends of the tube carriers 162 are        connected with the proton exchange membrane 12, whereby the        proton conductor 166 filled in the tube carriers 162 directly        contacts the proton exchange membrane 12.

In the step S1, a material of the porous template 20 is not limited andcan form the tube carriers 162. The porous template 20 can be an aluminatemplate or a silicon dioxide template. In one embodiment, the poroustemplate 20 is an alumina template. The tube carriers 162 formed in theholes of the porous template 20 can define a plurality of reaction gaspassages. A shape, a diameter, and the location of the holes of theporous template 20 can be set according to the shape, the diameter, andthe location of the desired tube carriers 162. If the tube carriers 162are to be uniformly distributed, substantially parallel to each other,and spaced from each other, the holes of the porous template 20 are alsouniformly distributed, substantially parallel to each other, and spacedfrom each other. If the tube carriers 162 are to be disorderlydistributed, the holes of the porous template 20 are also disorderlydistributed. The porous template 20 has two opposite surfaces. Aplurality of openings exists on at least one surface of the poroustemplate 20 to expose the plurality of holes. One opening corresponds toone hole. In one embodiment, the holes of the porous template 20 extendfrom one surface to the other surface of the porous template 20. Adiameter of the hole of the porous template 20 can be in a range fromabout 10 nm to about 10 μm. In one embodiment, the diameter of the holeof the porous template 20 is in a range from about 50 nm to about 300nm. In one embodiment, the holes of the porous template 20 are uniformlydistributed, substantially parallel to each other, and spaced from eachother, the holes are straight line shaped, a distance between theadjacent holes is in a range from about 10 nm to about 50 μm. Athickness of the porous template 20 can be in a range from about 1 μm toabout 100 μm. In one embodiment, the diameter of the holes of the poroustemplate 20 is about 100 nm, the distance between the adjacent holes isabout 100 nm, and the thickness of the porous template 20 is about 7 μm.

In the step S2, the tube carriers 162 can be carbon nanotubes, titaniumdioxide nanotubes, zinc oxide nanotubes, cobalt oxide nanotubes, orvanadic oxide nanotubes. The tube carriers 162 can be formed in theholes by vaporization method, chemical vapor deposition, sol-gel method,and immersing method.

In one embodiment, the tube carriers 162 are formed by the immersingmethod. The immersing method includes the following steps: S11,providing a carbon source compound solution and immersing the poroustemplate 20 in the carbon source compound solution; and S12, removingthe porous template 20 from the carbon source compound solution, andannealing the porous template 20 to form the carbon nanotubes in theholes of the porous template 20.

In the step S11, the carbon source compound solution is formed bydissolving a carbon source compound in a solvent. In one embodiment, thecarbon source compound is dissolved in water or volatile organicsolvent. The water can be distilled water or deionized water. Thevolatile organic solvent can be ethanol, propyl alcohol, or acetone. Thecarbon source compound can be decomposed to form carbon by annealing. Inone embodiment, the carbon source compound is decomposed to formamorphous carbon. The carbon source compound can be oxalic acid,sucrose, glucose, phenolic resin, polyacrylic acid, polyacrylonitrile,polyoxyethylene, or polyvinyl alcohol. If a concentration of the carbonsource compound solution is too large, the carbon source compoundsolution cannot sufficiently immerse in the holes of the porous template20. If the concentration of the carbon source compound solution is toosmall, a viscosity of the carbon source compound solution is too smalland the carbon nanotubes cannot be sufficiently formed. In addition, aporosity of the tube carriers 162 can be influenced by the concentrationof the carbon source compound solution. If the concentration of thecarbon source compound solution is small, the porosity of the tubecarriers 162 is large. If the concentration of the carbon sourcecompound solution is large, the porosity of the tube carriers 162 issmall. In one embodiment, the concentration of the carbon sourcecompound solution is in a range from about 0.05 g/mL to about 1 g/mL.The porous template 20 can be immersed in the carbon source compoundsolution for about 5 minutes to about 5 hours, so that the carbon sourcecompound solution can sufficiently immerse in the holes of the poroustemplate 20. In one embodiment, the alumina template is immersed in theoxalic acid solution having the concentration of 0.2 g/mL for about 1hour. In addition, the immersing period can be decreased by applying apressure on the carbon source compound solution.

In the step S12, the porous template 20 can be further washed by wateror volatile organic solvent and dried, after the porous template 20 istaken out from the carbon source compound solution. Specifically, thewashed porous template 20 can be heated under vacuum. A heatingtemperature can be in a range from about 60° C. to about 100° C. Aheating period can be in a range from about 30 minutes to about 6 hours.In one embodiment, the washed porous template 20 is heated to about 80°C. for about 3 hours. The porous template 20 can be annealed by thefollowing steps: disposing the porous template 20 in the heating stoveunder protective atmosphere; calcining the porous template 20 to apredetermined temperature, thereby decomposing the carbon sourcecompound to form carbon nanotubes composed of amorphous carbon. Thecalcining period and the calcining temperature can be set according tothe kinds of the carbon source compound. In one embodiment, the carbonsource compound is oxalic acid, the porous template 20 is calcined toabout 100° C. to about 150° C. under a heating speed of about 1°C./minutes to about 5° C./minutes. The temperature of the poroustemplate 20 is kept at about 100° C. to about 150° C. for about 1 hourto about 3 hours. The porous template 20 is then continuously calcinedto about 400° C. to about 600° C. at a rate of about 1° C./minutes toabout 5° C./minutes. The temperature of the porous template 20 is keptat about 400° C. to about 600° C. for about 2 hours to about 8 hours.The porous template 20 is then cooled to room temperature.

In the step S3, the catalyst particles 164 can be precious metalparticles having high catalytic activity. The material of the catalystparticles 164 can be Pt, Pd, Au, or Ru. In one embodiment, the catalystparticles 164 are Pt particles. The catalyst particles 164 can be formedby the following immersing the porous template 20 defining the tubecarriers 162 in a solution containing catalyst ions; and reducing thecatalyst ions to form the catalyst particles 164 uniformly adsorbed onthe inner walls of the tube carriers 162. In one embodiment, the Ptcatalyst particles are formed by the following steps: S21, providing aplatinic chloride (H₂PtCl₆) solution, and immersing the porous template20, having the tube carriers 162 formed therein, in the H₂PtCl₆solution, wherein a PH value of H₂PtCl₆ solution is adjusted toalkalescence; S22, adding a reduction object into the H₂PtCl₆ solutionto form a mixture, and heating the mixture to cause a redox reactionbetween the H₂PtCl₆ and the reduction object, thereby forming Ptcatalyst particles on the tube carriers 162.

In the step S21, the H₂PtCl₆ solution is formed by dissolving theH₂PtCl₆ in distilled water or volatile organic solvent. A concentrationof the H₂PtCl₆ solution can be set according to the quantity of theformed catalyst particles 164. A molar concentration of the H₂PtCl₆solution can be in a range from about 0.01 mol/L to about 0.1 mol/L. Inone embodiment, the molar concentration of the H₂PtCl₆ solution is 0.05mol/L. The PH value of the H₂PtCl₆ solution can be adjusted bydissolving an alkaline compound in the H₂PtCl₆ solution. The alkalinecompound can be Na₂CO₃, NaOH, or KOH. The PH value of the H₂PtCl₆solution can be adjusted in a range from about 8 to about 9. In the stepS22, the reduction object can be formaldehyde (HCHO), formic acid(HCOOH), or potassium borohydride (KBH₄). A quantity of the reductionobject can be set to reduce the Pt ions of the H₂PtCl₆ solution intometal Pt particles. A heating temperature can be in a range from about50° C. to about 70° C. Furthermore, a protective gas can be introducedduring the heating process. The protective gas can be nitrogen gas orargon gas. The diameter of the formed catalyst particles 164 can be in arange from about 1 nm to about 8 nm. After step S22, the porous template20 can be taken out, washed by the distilled water or volatile organicsolvent, and then dried.

In the step S4, the proton conductor 166 can be fused into liquid, or bedissolved in a solvent to form a proton conductor solution. The protonconductor 166 can be filled in the tube carriers 162 by two methods. Thefirst method is flatly disposing the porous template 20 on the fusedproton conductor 166 or the proton conductor solution. The second methodis pouring the fused proton conductor 166 or the proton conductorsolution on the surface exposing the holes of the porous template 20.

In the first method, the surface exposing the holes of the poroustemplate 20 is in contact with the fused proton conductor 166 or theproton conductor solution, and the fused proton conductor 166 or theproton conductor solution is gradually immersed into the tube carriers162 in the holes of the porous template 20 under a capillary force. Inthe second method, the fused proton conductor 166 or the protonconductor solution gradually flows into the tube carriers 162 in theholes of the porous template 20. A vacuum pump can be used to pump thefused proton conductor 166 or the proton conductor solution, by whichthe fused proton conductor 166 or the proton conductor solution canrapidly flow in the tube carriers 162 in the holes of the poroustemplate 20.

If the tube carriers 162 in the holes of the porous template 20 arefilled with the fused proton conductor 166, the fused proton conductor166 can be solidified by standing in room temperature or low temperatureheating for a predetermined period. If the tube carriers 162 in theholes of the porous template 20 are filled with the proton conductorsolution, the solvent in the proton conductor solution can be filtratedout, and the remaining proton conductor 166 can then be solidified bystanding in room temperature or low temperature heating for apredetermined period. In addition, the porous template 20 filled withthe proton conductor 166 can be washed by the distilled water orvolatile organic solvent, and then vacuum dried. In one embodiment, theproton conductor 166 is perfluorosulfonic acid resin. Before filling theperfluorosulfonic acid resin in the tube carriers 162 in the holes ofthe porous template 20, the perfluorosulfonic acid resin is heated to amolten state.

In the step S5, after hot pressing the laminated structure, thelaminated structure is integrated together and cannot be separated. Theproton conductor 166 in the tube carriers 162 is directly connected withthe proton exchange membrane 12.

In the step S6, the porous templates 20 can be removed by corrosiontechnology. In one embodiment, the porous template 20 is an aluminatemplate, the laminated structure is immersed in a NaOH water solutionor a H₃PO₄ water solution to erode the alumina template. In oneembodiment, a molar concentration of the NaOH water solution is in arange from about 0.5 mol/L to about 4 mol/L. A mass ratio of the H₃PO₄water solution is in a range from about 3% to about 15%. After removingthe alumina template, the orderly oriented tube carriers 162 aredisposed on the surface of the proton exchange membrane 12.

Depending on the embodiment, certain steps of methods described may beremoved, others may be added, and the sequence of steps may be altered.It is also to be understood that the description and the claims drawn toa method may include some indication in reference to certain steps.However, the indication used is only to be viewed for identificationpurposes and not as a suggestion as to an order for the steps.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the present disclosure.Variations may be made to the embodiments without departing from thespirit of the present disclosure as claimed. Elements associated withany of the above embodiments are envisioned to be associated with anyother embodiments. The above-described embodiments illustrate the scopeof the present disclosure but do not restrict the scope of the presentdisclosure.

What is claimed is:
 1. A bio-fuel cell comprising: at least one bio-fuelcell element comprising: a membrane electrode assembly comprising: ananode and a cathode, the cathode comprising a catalyst layer comprisinga plurality of tube carriers having electron conductibility, a pluralityof catalyst particles uniformly adsorbed on a wall of each of theplurality of tube carriers, and a proton conductor filled in each of theplurality of tube carriers, the plurality of tube carriers cooperativelydefining a plurality of reaction gas passages for transferring reactiongas to surfaces of the plurality of catalyst particles; and a protonexchange membrane sandwiched between the anode and the cathode, a firstend of each of the plurality of tube carriers being connected with theproton exchange membrane, the proton exchange membrane being in contactwith the proton conductor filled in each of the plurality of tubecarriers; a guide plate disposed on a surface of the cathode away fromthe proton exchange membrane; and an anode container filled withbiofuel, wherein the anode is immersed in the biofuel of the anodecontainer.
 2. The bio-fuel cell as claimed in claim 1, wherein theplurality of reaction gas passages comprise a plurality of gaps definedbetween the plurality of tube carriers.
 3. The bio-fuel cell as claimedin claim 1, wherein the plurality of reaction gas passages comprise aplurality of holes defined in the wall of each of the plurality of tubecarriers.
 4. The bio-fuel cell as claimed in claim 1, wherein theplurality of tube carriers are disorderly arranged.
 5. The bio-fuel cellas claimed in claim 1, wherein a shape of each of the plurality of tubecarriers in the catalyst layer is straight, curvy, V-shaped, orY-shaped.
 6. The bio-fuel cell as claimed in claim 1, wherein theplurality of tube carriers is spaced from each other.
 7. The bio-fuelcell as claimed in claim 6, wherein the plurality of tube carriers issubstantially parallel to each other and substantially perpendicular toa surface of the proton exchange membrane.
 8. The bio-fuel cell asclaimed in claim 7, wherein a distance between every two adjacent tubecarriers of the plurality of tube carriers is less than 50 μm.
 9. Thebio-fuel cell as claimed in claim 1, wherein the plurality of tubecarriers are selected from the group consisting of carbon nanotubes,titanium dioxide nanotubes, zinc oxide nanotubes, cobalt oxidenanotubes, vanadic oxide nanotubes, and any combination thereof.
 10. Thebio-fuel cell as claimed in claim 1, wherein the plurality of tubecarriers are carbon nanotubes composed of amorphous carbon.
 11. Thebio-fuel cell as claimed in claim 1, wherein a diameter of each of theplurality of tube carriers is in a range from about 10 nm to about 10μm.
 12. The bio-fuel cell as claimed in claim 1, wherein a wallthickness of each of the plurality of tube carriers is in a range fromabout 2 nm to about 15 nm.
 13. The bio-fuel cell as claimed in claim 1,wherein the plurality of catalyst particles are selected from the groupconsisting of Pt particles, Pd particles, Au particles, Ru particles,and any combination thereof.
 14. The bio-fuel cell as claimed in claim1, further comprising a gas diffusion layer disposed on a second end ofeach of the plurality of tube carriers, and the gas diffusion layer iselectrically contacting the walls of the plurality of tube carriers. 15.The bio-fuel cell as claimed in claim 1, wherein at least one flow guidegroove is defined on a surface of the guide plate near the protonexchange membrane, the at least one bio-fuel cell element furthercomprises a gas supply and suction device connected with the at leastone flow guide groove of the guide plate to introduce the reaction gasinto the cathode.
 16. The bio-fuel cell as claimed in claim 1, furthercomprising a current collecting plate used to collect and conductelectrons, wherein the current collecting plate electrically contactsthe guide plate.
 17. The bio-fuel cell as claimed in claim 1, whereinthe anode comprises a catalyst carrier and an enzyme catalystdistributed on the catalyst carrier.
 18. A bio-fuel cell comprising: aplurality of bio-fuel cell elements connected with each other, each ofthe plurality of bio-fuel cell elements comprising: a membrane electrodeassembly comprising: an anode and a cathode, the cathode comprising acatalyst layer comprising a plurality of tube carriers having electronconductibility, a plurality of catalyst particles uniformly adsorbed onan inner wall of each of the plurality of tube carriers, and a protonconductor filled in each of the plurality of tube carriers, theplurality of tube carriers cooperatively defining a plurality ofreaction gas passages for transferring reaction gas to surfaces of theplurality of catalyst particles; and a proton exchange membranesandwiched between the anode and the cathode, one end of each of theplurality of tube carriers being connected with the proton exchangemembrane, the proton exchange membrane being in contact with the protonconductor filled in each of the plurality of tube carriers; a guideplate disposed on a surface of the cathode away from the proton exchangemembrane; and an anode container filled with biofuel, the anode beingimmersed in the biofuel of the anode container.
 19. The bio-fuel cell asclaimed in claim 18, wherein the plurality of bio-fuel cell elementsconnected with each other in series, and the anode of one bio-fuel cellelement is electrically connected with the cathode of another bio-fuelcell element.
 20. The bio-fuel cell as claimed in claim 18, wherein theplurality of bio-fuel cell elements connected with each other inparallel, anodes of the plurality of bio-fuel cell elements areelectrically connected with each other, and cathodes of the plurality ofbio-fuel cell elements are electrically connected with each other.